This thread is exactly the thread I was looking for.
15.17 When the ball has been clearly won by a team at the ruck, and is available to be played, the referee calls “use it”, after which the ball must be played away from the ruck within five seconds.
"If a Ruck, then a player in the Ruck may unbind and pick up the ball as long as both feet are behind the ball."
"You can be behind the ruck and pick up the ball, but you can't be IN the ruck and pick the ball up"
So the condition that must be satisfied for someone who WAS part of the ruck when it was formed, is that they must first find themselves in a position where both feet are behind the ball before they unbind. Unbinding at this moment means they are no longer part of the ruck and are allowed to pick the ball up that is in front of them, run with it, pass it or kick it, essentially as if they were a scrum half?
This means that the moment the player unbinds , just before picking up the ball, would also signal that the ruck has ended and the ball is in open play. Which means there is no gate any more and any defender can pick up the ball as long as they are also behind the ballz, from their perspective (EXCEPT 15.18 A player who is, or WAS part of the ruck may not play an opponent who is near it (within 1m), and who is attempting to play the ball away.)? So presumably attempting to play the ball away IS kicking or passing but NOT running with the ball - if the player who unbound , picked up the ball and ran with it maybe tackled by anyone who WAS part of the ruck regardless of whether they are within 1m of the ball carrier or not.
However, this is interesting though:
15.16 Players must not:
g. Take any action to make opponents believe that the ruck has ended when it has not.
Sanction:Free-kick.
So if my conclusion of 15.17 above is correct, then a player in the ruck who unbinds and picks up the ball could ALSO be deemed as someone who is making the opponents believe the ruck has ended when it may not have. Why? because how are the opponents to know whether the ruck has ended, they are unlikely to be able to see that he unbound when both feet were behind the ball. It's a ruck, you can't see the ball and know whose feet belong to who! As such, could or should the referee award the opponents a free kick against someone unbinding from the ruck then picking up the ball using this rule? The TMO in your example obviously disagree. If the referee shouts "use it" before the player unbinds, then obviously it signals to the opposition that the ruck has been won and any unbinding signifies open play has commenced.
